Brinell scale

The Brinell scale characterizes the indentation hardness of materials through the scale of penetration of an indenter, loaded on a material test-piece. It is one of several definitions of hardness in materials science.

Proposed by Swedish engineer Johan August Brinell in 1900, it was the first widely used and standardised hardness test in engineering and metallurgy. The large size of indentation and possible damage to test-piece limits its usefulness.

The typical test uses a 10 millimetres (0.39 in) diameter steel ball as an indenter with a 3,000 kgf (29 kN; 6,600 lbf) force. For softer materials, a smaller force is used; for harder materials, a tungsten carbide ball is substituted for the steel ball. The indentation is measured and hardness calculated as:

\mbox{BHN}=\frac{2P}{\pi D ({D-\sqrt{(D^2-d^2)})}}

where:

P = applied force (kgf)
D = diameter of indenter (mm)
d = diameter of indentation (mm)

The BHN can be converted into the ultimate tensile strength (UTS), although the relationship is dependent on the material, and therefore determined empirically. The relationship is based on Meyer's index (n) from Meyer's law. If Meyer's index is less than 2.2 then the ratio of UTS to BHN is 0.36. If Meyer's index is greater than 2.2, then the ratio increases.[1]

BHN is designated by the most commonly used test standards (ASTM E10-08[2] and ISO 6506-1:2005[3]) as HBW (H from hardness, B from brinell and W from the material of the indenter, tungsten (wolfram) carbide). In former standards HB or HBS were used to refer to measurements made with steel indenters.

HBW is calculated in both standards using the SI units as

\mbox{HBW}=0.102 \frac{2F}{\pi D ({D-\sqrt{(D^2-d^2)})}}

where:

F = applied force (N)
D = diameter of indenter (mm)
d = diameter of indentation (mm)

Contents

Common values

When quoting a Brinell hardness number (BHN or more commonly HB), the conditions of the test used to obtain the number must be specified. The standard format for specifying tests can be seen in the example "HBW 10/3000". "HBW" means that a tungsten carbide (from the chemical symbol for tungsten) ball indenter was used, as opposed to "HBS", which means a hardened steel ball. The "10" is the ball diameter in millimeters. The "3000" is the force in kilograms force.

The hardness may also be shown as XXX HB YYD^2. The XXX is the force to apply (in kgf) on a material of type YY (5 for aluminum alloys, 10 for copper alloys, 30 for steels). Thus a typical steel hardness could be written: 250 HB 30D^2. It could be a maximum or a minimum.

Brinell hardness numbers
Material Hardness
Softwood (e.g., pine) 1.6 HBS 10/100
Hardwood 2.6–7.0 HBS 1.6 10/100
Lead 5.0 HB (pure lead; alloyed lead typically can range from 5.0 HB to values in excess of 22.0 HB)
Aluminium 15 HB
Copper 35 HB
Mild steel 120 HB
18-8 (304) stainless steel annealed 200 HB[4]
Glass 1550 HB
Hardened tool steel 1500–1900 HB
Rhenium diboride 4600 HB
Note: Standard test conditions unless otherwise stated

Standards

See also

References

Notes

  1. ^ Tabor, p. 17.
  2. ^ ASTM E10 - 08 Standard Test Method for Brinell Hardness of Metallic Materials
  3. ^ ISO 6506-1:2005 Metallic materials - Brinell hardness test - Part 1: Test method
  4. ^ 304: the place to start, http://www.assda.asn.au/index.php?option=com_content&task=view&id=65&Itemid=91, retrieved 2009-03-31 .

Bibliography

External links